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Recently, the process of space-time block coding (STBC) recognition has found applications in a wide range of wireless transmissions. Numerous investigations on this topic have been developed for single-carrier transmissions and a few studies have been introduced for orthogonal frequency division multiplexing (OFDM) transmissions. The previous research work in the literature has focused on exploiting the space-time redundancy to blindly estimate the type of STBC signal. In this work, we propose a new approach to design a STBC recognizer for OFDM transmissions by taking benefits from the a posteriori probabilities provided by a channel decoder. The mathematical treatments have shown that the exact maximum-likelihood (ML) solution to this problem is computationally demanding in the absence of a closed form. Therefore, we settle for the expectation-maximization (EM) algorithm as a low-complexity procedure to perform STBC recognition. In addition, we develop a channel estimation algorithm to be integrated into the proposed recognition algorithm. Simulation results are presented to confirm the theoretical analysis, with exhibiting superior recognition performance over the state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

The problem of automatic modulation identification (AMI) is one of the main challenges that faces orthogonal frequency division multiplexing (OFDM) software-defined radio (SDR) systems. The previously reported studies of this aspect have limited to uncoded transmission; however, practical systems typically employ error-correcting codes. In this work, we exploit the properties of bit-interleaved coded modulation iterative decoding (BICM-ID) schemes, which are widely used in wireless communications systems, to develop a novel AMI algorithm for OFDM-SDR systems. Since the exact maximum-likelihood (ML) solution is intractable in practice, we resort to an expectation-maximization (EM) procedure as a statistical analysis tool. The proposed identification algorithm works in an iterative fashion, in which the soft information provided by the channel decoder of BICM-ID scheme is utilized as a priori information to the proposed identifier. The results indicate that the identification performance of the proposed algorithm achieves a significant improvement with iterations and outperforms that of the conventional uncoded algorithms. These favorable results are achieved with reduced processing time and acceptable sensitivity to transmission impairments, such as clock timing offset, frequency offset, Doppler shift, and phase noise. [ABSTRACT FROM AUTHOR]

In this letter, we address the problem of estimating the integer part of carrier frequency offset (CFO) in space frequency block codes (SFBCs) systems with orthogonal frequency division multiplexing (OFDM) modulation schemes. We derive a maximum-likelihood (ML) estimator assuming that the receiver has two receive antenna, and then we extend the analytical analysis to an arbitrary number of receive antennas. The proposed estimator is designed in a way that exploits the additional two-dimensional space-frequency redundancy provided by SFBCs. Because of its popularity, Alamouti code is chosen to be the code of interest. However, a similar analytical treatment could be applied to any other code. The computational complexity analysis and Monte Carlo experiments are carried out to verify effectiveness of the proposed estimator for practical applications. [ABSTRACT FROM AUTHOR]

In this letter, we develop a channel estimation algorithm for a downlink multi-carrier code division multiple access system in the context of two-path successive relaying transmission. We employ the expectation maximization tool to get the maximum likelihood estimate of the channel impulse responses of the direct and relays links. The proposed algorithm proceeds in an iterative structure and utilizes the soft information given by the demodulator as a priori probabilities to refine the estimation process, without causing overhead to the demodulation execution. The simulation experiments are carried out to assess the effectiveness of the proposed estimator. [ABSTRACT FROM AUTHOR]

This paper proposes two new data detection algorithms for decode-and-forward alternate-relaying cooperative communication systems. These algorithms are discussed in the context of bit-interleaved coded modulation transmission with a multiple-antenna destination. The interference signal, resulting from the concurrent transmission of the source and one of the relays, is exploited as a beneficial resource to develop an optimal data detection algorithm. We show that the optimal algorithm can be implemented by parallel demappers, each based on a family of Bahl, Cocke, Jelinek, and Raviv algorithms, connected to parallel decoders in an iterative way. Due to the need to buffer the entire frame before decoding, the optimal algorithm suffers from long processing time. A suboptimal algorithm is also proposed to avoid this problem, where each packet is decoded by using two consecutive received packets. The suboptimal algorithm reduces processing time, complexity, bandwidth loss, and memory size with a slight increase in the bit error rate (BER). The BER performance of the proposed algorithms is evaluated via Monte Carlo simulations, and the results indicate their effectiveness in improving the BER performance. [ABSTRACT FROM AUTHOR]